rename max backgroud app property (again)

This reverts commit a30f6eea9ee71091c723896da870615eb500651d.

And the circle closes. :P
http://review.cyanogenmod.org/#/c/34367/
https://github.com/CyanogenMod/android_frameworks_base/commit/9f617a00eb5b7b8fa89f3b61182ab8c8ff94097b
http://review.cyanogenmod.org/#/c/47288/
http://review.cyanogenmod.org/#/c/48642/

Change-Id: I779d53972a4a3773b24e740a73732b24669b9ba3